The present invention relates generally to the fields of polymers and high-density compositions. More particularly, it concerns materials that may act as a replacement for lead in applications requiring lead""s high density, but where the toxic effects of lead are undesirable. Further, the high-density composites of the present invention may be employed in any application where a high-density material is required.
Shotshells containing lead shot pellets in current use have demonstrated highly predictable characteristics particularly when used in plastic walled shot shells with plastic shotcups. These characteristics include uniform pattern densities with a wide variety of shotgun chokes and barrel lengths, and uniform muzzle velocities with various commercially available smokeless powders. All of these characteristics contribute to lead shots efficacy on game, particularly upland game and bird hunting. This characteristic predictability has also enabled the user to confidently select appropriate shot sizes and loads for his or her own equipment for hunting or target shooting conditions. Steel shot has a lower density than lead and currently does not offer the same predictability. Each hunting season is prefaced with new commercial offerings of ammunitions to ameliorate one or more of the disadvantages associated with the use of steel shot which disadvantages include lower muzzle velocities, poor pattern density and lower energy per pellet delivered to the target. Most, if not all, of these disadvantages could be overcome by the use of shot shell pellets which approximated the specific gravity of the lead or lead alloy pellets previously employed in most shot shell applications. With the increased concern for the perceived adverse environmental impact resulting from the use of lead containing pellets in shotgun shot shells there has been a need for finding a suitable substitute for the use of lead that addresses both the environmental concerns surrounding the use of lead while retaining the predictable behavior of lead in hunting and target shooting applications.
Presently steel is typically employed as a non-toxic material in shot. Steel shot pellets generally have a specific gravity of about 7.5 to 8.0, while lead and lead alloy pellets have a specific gravity of about 10 to 11. Further, lead is more ductile and its greater weight per unit volume permits its use with relatively fast burning smokeless powder and a variety of barrel chokes. This produces an effective predictable muzzle velocity for various barrel lengths and provides a uniform pattern at pre-selected test distances. These are important criteria for both target shooting such as sporting clays; trap and skeet as well as upland game and bird hunting. Conversely, steel shot pellets do not deform; this has necessitated the production of shot shells having two or more pellet sizes to produce better pattern densities. Unfortunately, the smaller pellet sizes, while providing better patterns, do not deliver as much energy as do the larger pellets under the same powder load conditions. Also, because steel shot is not as ductile as lead it can scratch and scrape standard shotgun barrels requiring special barrels to be designed for steel shot.
Other alloys than steel such as a tungsten based alloy have been substituted as an alternative material to lead in shot pellets. Tungsten powder is relatively non-toxic and is suitable for commercial applications. However because solid metallic tungsten is a very hard material and melts at an extremely high temperature (approx. 3410 C., the highest melting point of all metals) it requires a large amount of heating and as a result is very expensive to mold and cast. The present formulations allows for injection and compression molding thus avoiding difficulties that may be encountered with working with pure tungsten. Alloy compositions including tungsten therein and other metals such as iron melt at a slightly lower temperature 3000xc2x0 F. but this alloy still requires significant energy input to melt the alloy see U.S. Pat. No. 5,527,376 to Amick et al. The cost of energy used to melt these compositions is prohibitive to using a sintering process in forming a tungsten alloy
Further, the dynamics of the shot pellets are significantly affected by pellet hardness, density and shape, and it is important in finding a suitable substitute for lead pellets to consider the interaction of all those factors. However, the pattern density and shot velocity of lead shot is critical for on-target accuracy and efficacy have thus far been nearly impossible to duplicate with environmentally non-toxic, safe economical substitutes.
At target shoot areas expensive cleanup procedures must be employed that provide only a temporary solution to the problem. A non-toxic cost effective replacement projectile core material is required to enable firing ranges to remain open and to eliminate costly cleanup procedures. The density of the projectile should be close to that of a lead projectile for realistic performance simulation. Materials of a lower density decrease projectile range and penetration.
In addition, there is mounting concern over the use of lead shot for bird hunting, due to ingestion of the shot by birds and other animals as well as contamination of wetland areas. Indeed there has been legislation in the United States and other countries which bans the use of lead shots in waterfowl shots.